Microporous anisotropic phase inversion membranes from bisphenol-A polycarbonate: Study of a ternary system (original) (raw)
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Journal of Applied Polymer Science, 2002
Phase inversion is a very flexible technique to obtain membranes with a large sort of morphologies. Membrane properties can vary greatly depending on the kind of polymer system used. Bisphenol A polycarbonate (PC) could be used as a phase inversion membrane base polymer, and presents very good properties. Nevertheless, very little information on membrane preparation using PC and the phase inversion process can be found in the literature. In this work flat-sheet microporous membranes were obtained by the phase inversion process using the immersion precipitation technique. A new polymer system was studied, consisting of polycarbonate, N-methyl-2-pyrrolidone as solvent, water as the nonsolvent, and an additive. The influence of some parameters on membrane morphology, such as polymer solution composition, exposition time before immersion into the precipitation bath, and the kind of additive was investigated. Precipitation was followed using light transmission experiments and membrane morphology was observed through Scanning Electron Microscopy (SEM). The viscosity and cloud points of all polymer solutions were also determined. The results were related to the studied synthesis parameters, using the basic principles of membrane formation by the phase inversion technique, looking forward to establishing criteria to control the morphology of flat-sheet membranes using polycarbonate as the base polymer. The results showed that both additives were able to increase pore interconnectivity and even suppress macrovoid formation. The decrease in the miscibility region of the polymer system and increase in mass transfer resistance are found to be the determining factors during polymer solution precipitation.
Journal of Membrane Science, 1991
Microporous polypropylene films were produced from nucleated and non-nucleated melt-blends of i&a&c polypropylene (iPP) and dotriacontane (C,,H,) using non-isothermal thermally-induced phase separation. Adipic acid was used as the nucleating agent. The morphology of these microporous iPP films as determined by thermal optical microscopy and scanning electron microscopy is reported. The effect on film structure of diluent crystallization is also shown.
1996
Structural characteristics in membranes formed by diffusion induced phase separation processes are discussed. Established theories on membrane formation from ternary systems can be extended to describe the effects of high or low molecular weight additives. A mechanism for the formation of nodular structures in the top layer of ultrafiltration membranes is presented. In the last part structures arising from polymer crystallization during immersion precipitation are discussed.
Polymer, 2009
Microporous membranes were prepared by thermally induced phase separation (TIPS) using different tailor-made syndiotactic polypropylenes (sPP) synthesized by metallocene catalysts. The phase diagrams of sPP samples in diphenyl ether (DPE) were determined. The polymer microstructure effect on the thermodynamic and kinetic properties of the sPP-DPE systems were also determined and correlated with membrane pore size. The crystal structure which developed in the matrix of the porous membranes was investigated by wide-angle X-ray diffraction (WXRD). The cloud points were found to be slightly affected by molecular weight (M w) and the influence of syndiotacticy was negligible. The dynamic crystallization curves depended solely on the syndiotacticity of the samples, shifting to lower temperatures as the stereoregularity of the sPP decreased, and no relation with M w was found. The viscosity of sPP-DPE solutions increased with M w and stereoregularity of the sPP. Membrane pore sizes were correlated with droplet growth period, crystallization behaviour, and sample viscosity, the latter being an important parameter for low polymer solution concentration (15 wt%) but not so at higher concentration (40 wt%). The results showed that by controlling polymer microstructure it is possible to control membrane pore size.
Formation of ordered micro-porous membranes
The European Physical Journal B, 1999
Regular micro-porous polymeric membranes have recently been discovered by rapidly evaporating a solution of CS2 containing poly(p-phenylene)-block-polystyrene [1]. 1,2-dichloroethane (a chlorated solvent in which polystyrene gel phase has never been observed) is also found to produce ordered structures, which definitively excludes eventual effect of the gelation process during the membrane formation. The observation of the solution surface during the solvent evaporation reveals the growing of micron-sized water droplets trapped at the surface and forming compact aggregates. The study of the solution/water interface shows that the water droplets profile is in agreement with the pore shape observed in the membranes. Moreover, the copolymer was found to precipitate at the interface, forming a layer encapsulating the droplets and preventing their coalescence. In that way, the final structure results from the droplets stacking under the action of large surface currents. Finally, we argue that the decisive element in the formation of ordered structures is the ability of the polymer to precipitate at the solution/water interface, which seems to be related the star-polymer microstructure.
Polymer, 2001
Two different types of membranes were prepared by immersion-precipitation process in two nonsolvent-DMSO-poly(ethylene-co-vinyl alcohol) (EVAL) systems. The effect of nonsolvent on the resulting membrane structure was studied via scanning electron microscopy. On using 2-propanol as the nonsolvent, the membrane showed a homogeneous particulate morphology. If the nonsolvent was changed to water, the membrane structure was a typically asymmetric structure while the particulate morphology was suppressed. In order to understand the change of the obtained membrane structures, the phase diagrams of water-DMSO-EVAL and 2-propanol-DMSO-EVAL systems were contrasted at 25ЊC. Both crystallization-induced gelation and liquid-liquid demixing were observed and equilibrium crystallization lines are always positioned above the binodal boundaries. Moreover, the precipitation rate of the EVAL solution in 2-propanol and water were examined by the light transmission experiments and the local composition profiles of membrane solution during membrane formation were analyzed by using a ternary mass transfer model. Based on both thermodynamic behaviors and kinetic properties, the membrane structures obtained were discussed in terms of the sequence and mechanism of phase transformations during membrane formation. ᭧
PVC Membranes Prepared via Non-Solvent Induced Phase Separation Process
Brazilian Journal of Chemical Engineering
Polyvinylchloride (PVC) based membranes are prepared via a phase inversion method using N,Ndimethylacetamide (DMAc) as solvent and water as precipitation bath. Polyvinylpyrrolidone (PVP) and lithium nitrate (LiNO 3) are used as additives. Experimental cloud point data and solution viscosity measurements are evaluated. Precipitation rates, transport properties and membrane morphology are quantified. Membranes with different morphologies and transport properties are prepared by changing the additive and its concentration, changing the PVC concentration and by varying the exposure time to the environment before immersion. An augment in PVC concentration increases solution viscosity, reduces precipitation rate and water permeability (J w), but it does not affect the instantaneous precipitation mechanism. PVC solutions with additives present higher viscosity values, slower light transmittance decay and membranes with higher J w (highest: ~1,350 L.h-1 .m-2. bar-1). LiNO 3 in the polymeric solution results in delayed demixing. A combination of high PVP concentration and environment exposure time changes the membrane morphology, suggesting spinodal demixing.
Desalination and Water Treatment, 2010
Microporous membranes of poly(1,4-butylene succinate) (PBS), which is a biodegradable biomass plastic, were prepared from PBS-chloroform solutions via nonsolvent and thermally induced phase separation with a coagulation bath of methanol. The permeation resistance of a membrane prepared from a 10% polymer solution at 25 C was more than 10 14 m-1. The membrane resistance decreased with increasing pre-incubation temperature. Retention of bacterial cells (0.7f  2.5 mm) decreased with increasing pre-incubation temperature. Increasing polymer concentration increased the permeation resistance and the retention of the cells. Membranes prepared from the 10% PBS solution pre-incubated at 47.5 C show a permeation resistance of 10 11 m-1 and retention of the bacterial cells of 99%. The PBS membranes will be useful in biosepartion processes as a prefilter that can be disposed by composting after use.